Internal control regions for transcription of eukaryotic tRNA genes.

We have identified the region within a eukaryotic tRNA gene required for initiation of transcription. These results were obtained by systematically constructing deletions extending from the 5' or the 3' flanking regions into a cloned Drosophila tRNAArg gene by using nuclease BAL 31. The ability of the newly generated deletion clones to direct the in vitro synthesis of tRNA precursors was measured in transcription systems from Xenopus laevis oocytes, Drosophila Kc cells, and HeLa cells. Two control regions within the coding sequence were identified. The first was essential for transcription and was contained between nucleotides 8 and 25 of the mature tRNA sequence. Genes devoid of the second control region, which was contained between nucleotides 50 and 58 of the mature tRNA sequence, could be transcribed but with reduced efficiency. Thus, the promoter regions within a tRNA gene encode the tRNA sequences of the D stem and D loop, the invariant uridine at position 8, and the semi-invariant G-T-psi-C sequence.